Pumps of this type are well known and comprise essentially a main hollow body of circular cross-section composed of coaxial portions of different diameter and housing all the pump operating members, including a coaxial stem projecting from one of the open ends of the main body. The stem is operated to deliver the substance contained in the bottle.
Specifically, delivery is obtained by pressing axially with the hand, in the direction of the main body, on a suitable knob fixed to the end of the stem projecting from the main body. The stem is returned to its rest or non-delivery position by the action of a return spring when the axial pressing action ceases.
A pump of this type is the subject of a further patent application in the name of the present applicant filed on the same date. The pump disclosed and claimed in that application comprises an overall tubular hollow main body for receiving the pump operating members, including an operating stem which projects from one end of the main body, and an element for retraining the stem within the main body. The retention element comprises a hole through which the stem passes. The hole is provided with an abutment element acting against the retention element, and the retention element comprises projections or recesses arranged to respectively snap-engage corresponding recesses or projections provided in or on the main body.
A problem of known pumps is to adjust the delivered quantity of the thick or liquid substance contained in the bottle or container on which such pumps are mounted.
Many methods have been devised for obtaining metered delivery of the substance. One of these methods uses one or more spacer rings coaxial to and superposed on the stem. The spacer rings are arranged to maintain a minimum predetermined distance between the retention element and a collar provided on the stem. By varying the number of such rings, the axial stroke of the stem is varied to thus vary the quanitiy of the substance delivered, although always using the same type of pump.
This method requires the intervention of an operator who has to manually position the number of rings needed to obtain the delivery of a required predetermined quantity of substance.
This operatin is not always simple to carry out, mainly because of having to work in small spaces with small elements, namely, the spacer rings.
Additionally, this operation obviously leads to a considerable cost increase.